This invention relates to forming a segment of elastomeric material to a predetermined length having tacky splicing surfaces at each end of the segment, the segment being formed from a strip of elastomeric material. In particular, the formation of a combination of low angle skived splicing surface with an abutment surface at each end of the segment is taught.
Elastomeric materials, particularly those used in the manufacture of tires, belts and other such industrial products requiring vulcanization of the elastomer are well known for having tacky surfaces which can readily be stuck together particularly prior to being completely cured or vulcanized. It is this very tacky surface feature that has enabled manufacturers to assemble various elastomeric components together in layers or composites of different shapes or compound materials without requiring additional adhesives or cements.
This pre-assembly of components is most common in the tire industry wherein layers of elongated elastomeric strips are cut to length and cylindrically wound and spliced upon a first stage building drum prior to being toroidally shaped and placed in a vulcanizing curing press.
Often the strips are formed from a homogeneous single elastomeric compound. Alternatively strips of tire components can be formed of multiple layers or composites having differing materials. Often one or more of the strips of tire components may have elastomeric material with reinforcing cords or fibers.
With the need to increase manufacturing efficiency, many of these strips of tire components are now formed as subassemblies or laminates having many components pre-assembled in sheets or strips of material as is described in U.S. Pat. No. 5,762,740. These laminated elastomeric materials when used are cut from elongated strips. In some cases the strips are sufficiently thick to permit the cut ends to be jointed in an abutting relation commonly referred to as butt splicing. Often the strips are cut on a skive angle and the ends are spliced as close as possible along the cut surfaces as is described in U.S. Pat. Nos. 5,746,101 and 5,746,102.
One advantage of butt splices are the cut to length segment has easy to detect ends making it possible to make a splice with no overlapping material. In the manufacture of tires, overlapping ends of material create mass distribution irregularities that can affect the ride and handling performance of the resultant tire. Butt splice""s one major drawback is the lack of adhesion at the joint due to the minimal contact area at the joint. Accordingly, butt splices can separate or disjoin at the splice during the shaping or curing of the tire if a sufficient surface area or thickness is not available. In those cases a splicing strip of gum rubber can be overlaid onto the splice joint again creating a mass distribution problem.
Skive cut surfaces or simply very thin strips are often lap spliced. In such a case, the components cut ends overlap slightly to provide increased surface area for joint adhesion. While lap splicing yields very good joint adhesion, the very existence of these joints contribute to tire non-uniformities such as sidewall undulations, uneven tread wear and tire imbalances as discussed above.
One of the most promising solutions to these problems is to provide splicing surfaces of sufficient area to enhance joint adhesion. The most promising solution has been to provide low angle skiving which forms cut angles less than 30 degrees relative to the plane of the material. This technique is particularly useful in strips of material having a moderate to thick cross-section such as the multi-layered laminates or composites. Such a technique of very low angle cutting is disclosed in PCT Application No. PCT/98/10387.
In cutting a non-reinforced tread strip for example it is relatively easy to achieve low skive angle cuts. Alternatively, low angle skive cutting cord reinforced strips or elastomeric composites with at least one layer of parallel cords can be much more difficult requiring special cutting techniques as disclosed in U.S. Pat. Nos. 5,746,101 and 5,746,102.
One of the problems associated with low angle cutting has been that it is not easy to align the cut ends, precisely. Unlike the butt splice, there is no clear indication when the cut ends are aligned. Low skive angle cuts are neither readily observable nor detectable as they are being joined. The one cut end when being attached to the other end obstructs the view. The stitched together joint is either overlapping or slightly underlapping. The very thin tips of the low angle skive cuts are easily deformed and damaged while the interior portion of the cut surface is barely discernable from the uncut surface, for these reasons the tire builder whether a man or an automated machine has a somewhat difficult time achieving a precise strip joint.
As a general rule the strip has a cut length slightly smaller than required which enables the strip to be stretched locally at the joint. This localized stretching can result in non-uniform cord spacing in the resultant tire. An example of splicing an elastomeric joint from a strip of elastomeric material can be found in U.S. Pat. No. 5,273,601. Stretching of strips to make a joint insures that entrapped air and ply or strip wrinkling is avoided. If the strip has parallel cords, as in the example of a radial ply used in the manufacture of a tire, localized stretching can change the cord spacing creating another non-uniformity. It is most important to note that uniformity is generally always desirable and that non-uniformities are almost always something to be avoided or eliminated in the manufacture of a tire splice.
The conventional wisdom in the manufacture of tires for example is that the number of splices should be minimized and if required at all the splices should be staggered around the circumference to minimize localized non-uniformities when multiple splices are circumferentially aligned.
One of the objects of the present invention is to provide a spliced joint that has a strip with ends that are easily and precisely located by employing a method and an apparatus for forming single or multi-component segments of elastomeric material of a predetermined length having ends exhibiting low angle splice surfaces for joint splicing in combination with abutment surfaces that are readily detectable by the tire builder.
Another object of the invention is to provide a method and apparatus that precisely achieves the same uniform joint repeatably and predictably wherein the strip of elastomeric material can be formed of a predetermined length without requiring the necessity of over stretching the strip.
Another object of the invention is to provide the above-mentioned splice joint on strips of material that have variations in cross-sectional thickness across the width of the strip or in flat strips having uniform thickness whether the strip is made of a single elastomeric material or a multi-layered components of different material compounds some of which may contain at least one layer of parallel cords oriented in a similar direction.
A method for forming a segment (10) of elastomeric material of a predetermined length L1 having tacking splicing surfaces (6) at each end (12, 14) from a strip (1) of elastomeric material is disclosed. The strip (1) has a length L, a width W, a maximum thickness t as measured across the width of the cross-section, a first side (2) and an opposite second side (4).
The method has the steps of a) forming a low angle skive surface (6) across the width W of the strip (1). The low angle skive surface (6) extends from a first side (2) of the strip (1) to a predetermined depth (d), (d) being less than the maximum thickness t of the strip (1); b) forming an abutment surface (8), the abutment surface (8) extending from the opposite second side (4) of the strip (1) across the width W of the strip (1) in a path substantially parallel to the low skive angle surface (6) and intersecting the low angle skive surface (6) thereby forming a first end (12) of the strip (1), the abutment surface (8) being at a first location S1, then repeating steps (a) and (b) at a second spaced location S2 spaced a predetermined distance L1 along the length L of the strip (1) from the location S1 thereby forming the segment (10) of elastomeric material of a predetermined length L1 and an opposite second end (14), wherein one of the ends (12, 14) has a low angle skive surface (6) extending inwardly along the length L1 of the segment relative to the ends abutment surface (8) at location S1 and the opposite end has a low angle skive surface (6) extending outwardly along the length L1 of the segment relative to the abutment surface (8) of that respective end (12 or 14) at location S2.
The method may further include the step of forming the segment (10) into a substantially cylindrical shape by the step of splicing the first and second ends (12, 14). The step of splicing the ends (12, 14) includes the step of contacting the abutment surfaces (8) of each end (12, 14) thereby establishing the circumferential length L1 of the cylindrical segment and applying pressure along the low angle skive surfaces (6) thereby forming a splice joint.
It should be understood that the step of forming a first end (12) of one segment (10) preferably simultaneously includes the step of forming a second end (14) of an adjacent segment (10) from the strip (1) of elastomeric material.
The preferred method further can have the step bending the strip (1) of elastomeric material across the width W of the strip (1) along a path (3) covering an area wherein a low angle skive surface (6) is to be formed. This bending the skive surface (6) of one end (12 or 14) separates and spaces it from the skive surface of the adjacent segment (10) as both surfaces (6) are being simultaneously formed. This prevents the tacky surfaces (6) from self-adhering back together as the surfaces (6) are being formed, a somewhat unique problem associated with uncured or partially cured rubber or elastomeric materials.
Alternatively a means to prevent the aforementioned reattachment of adjacent low angle skive surfaces (6) can be provided. The means can be vacuum apparatus to hold one surface (6) away from the other or a mechanical separations sheet or liner interposed between the surfaces (6) as they are formed.
In one method, the step of assembling a plurality of strips of tire components to form the strip (1) of elastomeric material, one or more of the strips of tire components being unvulcanized or partially vulcanized, is employed. In that method the assembly of tire components may include at least one strip of elastomeric material having reinforcing cords (22). The cords (22) are substantially parallel and oriented similarly in the direction of a path (3) formed across the width W of the strip (1) by the ends (12, 14) of the segments (10) being formed.
The method of forming a low angle skive surface (6) preferably includes step (a) of cutting the elastomeric strip (1). The first cutting is oriented at a predetermined skive angle xcex8, the first cutting being limited to the predetermined depth (d) and the step (b) of forming the abutment surface includes the step of making a second cut across the strip intersecting the first cut, thus, forming one end (12 or 14) of the segment (10).
In the case of forming low angle skive surfaces (6) with at least one layer of cord (22) reinforced material in the strip (1) a preferred method further includes the step (a) of cutting across the strip (1) in a direction of a cut path (3) substantially parallel and oriented similarly to the cords (22) using a first cutting element (120). The first cutting oriented at a desired skive angle xcex8, cuts to the depth (d). The depth (d) is substantially tangent to one or more cords (22). The step (b) of forming an abutment surface (8) includes the step of cutting across the strip (1) between two adjacent cords (22) with a second cutting element (122) intersecting the first cut at or near the depth (d), thus, forming one cut end of the segment (12 or 14). It is further preferred that the step of bending the elastomeric strip (1) along a path parallel to the cords (22) is used to prevent the surfaces from reattaching as previously mentioned. To accomplish this step, the strip (1) should be supported in the area of the bend path preferably on a side (4) opposite the side (2) of the first cut. This can best be accomplished by providing a contoured or inclined support (108) adjacent a substantially flat or planar support (110).
Additionally, when making a second cut across the strip (1), the cutting preferably initiates from a side (4) of the strip (1) opposite the first cut.
The first cut is made by a first cutting element (120), the first cutting element (120) preferably being an ultrasonic knife.
The second cut may be made by one or more second cutting elements (122). The second cutting element (122) may be any convention knife or blade and may be heated or ultrasonically vibrated to facilitate cutting. The second cutting preferably has the knife (122) passing between two adjacent cords (22) along the cutting path. The second cutting element is preferably oriented at an angle xcex2, xcex2 being at a high angle relative to the first or second side (2, 4) most preferably about normal. The second cut can either be initiated at an edge of the step or anywhere in-between. If two cutting elements (122) are used, they can initiate cutting midway in the strips width and extend in opposite directions to accomplish the cut.
The preferred apparatus (100) for cutting segments from a long strip (1) of multi-layered elastomeric material has a first cutting element (121), a second cutting element (122), a means (130) for moving the first and second cutting elements (121, 122) across the width of the strip (1) along a cut path (3), and a means for supporting (140) the strip. The apparatus (100) also has a means (104) for orienting and maintaining the first cutting element (120) at a desired skive angle xcex8. The means for supporting (140) preferably includes a first flat portion (110) and a second inclined or contoured portion (108).
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of a tire""s section height to its section width.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d or xe2x80x9cBead Corexe2x80x9d means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers.
xe2x80x9cBelt Structurexe2x80x9d or xe2x80x9cReinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 27xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cBias Ply Tirexe2x80x9d means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about a 25-65xc2x0 angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers.
xe2x80x9cBreakersxe2x80x9d or xe2x80x9cTire Breakersxe2x80x9d means the same as belt or belt structure or reinforcement belts.
xe2x80x9cCarcassxe2x80x9d means a laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread as viewed in cross section.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands, including fibers, which are used to reinforce the plies.
xe2x80x9cInner Linerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
xe2x80x9cInsertsxe2x80x9d means the crescentxe2x80x94or wedge-shaped reinforcement typically used to reinforce the sidewalls of runflat-type tires; it also refers to the elastomeric non-crescent-shaped insert that underlies the tread.
xe2x80x9cPlyxe2x80x9d means a cord-reinforced layer of elastomer-coated, radially deployed or otherwise parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial Ply Structurexe2x80x9d means the one or more carcass plies or which at least one ply has reinforcing cords oriented at an angle of between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cRadial Ply Tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSidewallxe2x80x9d means a portion of a tire between the tread and the bead.
xe2x80x9cSkivexe2x80x9d or xe2x80x9cskive anglexe2x80x9d refers to the cutting angle of a knife with respect to the material being cut; the skive angle is measured with respect to the plane of the flat material being cut.